SQL

Overview

SQL (Structured Query Language) is a standard programming language designed for managing relational databases. It allows users to perform various operations on databases, such as querying data, inserting, updating, and deleting records, creating and modifying database schema, and controlling access to the data.

Here are some key components and operations in SQL:

1. Data Definition Language (DDL):
   • CREATE TABLE: This command is used to create a new table in the database.
   • ALTER TABLE: This command is used to modifies an existing table by adding, modifying, or dropping columns or constraints.
   • DROP TABLE: This command is used to delete a table from the database.
   • CREATE INDEX: This command is used to create an index on one or more columns of a table to improve query performance.
   • DROP INDEX: This command is used to delete an index from the database.
2. Data Manipulation Language (DML):
   • SELECT: This command is used to retrieve data from one or more tables based on specified criteria.
   • INSERT INTO: This command is used to insert new records into a table.
   • UPDATE: This command is used to modify existing records in a table.
   • DELETE FROM: This command is used to delete records from a table based on specified criteria.
3. Data Query Language (DQL):
   • SELECT: Just like DML Select it also used to retrieve data from one or more tables. It can be used to filter, sort, aggregate, and join data.
4. Data Control Language (DCL):
   • GRANT: Gives specific privileges to database users.
   • REVOKE: Removes specific privileges from database users.
5. Transaction Control Language (TCL):
   • COMMIT: Saves changes made during the current transaction to the database.
   • ROLLBACK: Reverts the changes made during the current transaction.
   • SAVEPOINT: Sets a savepoint within a transaction.

SQL is used across various database management systems (DBMS), including:

• MySQL
• PostgreSQL
• SQLite
• Microsoft SQL Server
• Oracle Database
• IBM Db2
• MariaDB
• and many others.

SQL syntax may vary slightly between different database systems, but the basic principles remain consistent. It is a powerful tool for managing and querying structured data, making it a fundamental skill for developers and data professionals working with databases.

History of SQL

The history of SQL (Structured Query Language) dates back to the early 1970s and is closely tied to the development of relational database management systems (RDBMS). Here’s a brief overview of its evolution:

1. Early Database Systems (1960s):
   • Before the advent of SQL, database management systems (DBMS) were primarily hierarchical or network-based, with systems like IBM’s IMS and CODASYL’s database model dominating the landscape.
   • These systems required complex programming interfaces and lacked a standardized query language.
2. 1970s: Relational Model and SQL Birth:
   • In the early 1970s, Edgar F. Codd, a researcher at IBM, introduced the relational model for databases in his paper titled “A Relational Model of Data for Large Shared Data Banks.”
   • Codd’s relational model proposed a structured approach to organizing data into tables consisting of rows and columns, with relationships defined between tables.
   • In 1974, IBM developed System R, one of the earliest RDBMS implementations based on Codd’s relational model.
   • Structured Query Language (SQL) was created by Donald D. Chamberlin and Raymond F. Boyce at IBM Research in the mid-1970s as a way to interact with the relational model.
   • The initial version of SQL, called SEQUEL (Structured English Query Language), was designed to manipulate and retrieve data stored in IBM’s System R.
3. 1970s-1980s: Standardization and Commercialization:
   • SQL quickly gained popularity within IBM and became a key component of its database products.
   • In 1979, the first SQL standard, known as SQL-79, was published by ANSI (American National Standards Institute). This standard laid the foundation for future versions of SQL.
   • The commercialization of SQL-based RDBMS began in the late 1970s and early 1980s with products like Oracle Database, Ingres, and Sybase SQL Server entering the market.
   • These early implementations of SQL varied in syntax and functionality, leading to challenges in portability and interoperability.
4. 1980s-1990s: SQL Becomes Standardized:
   • In 1986, SQL-86 (also known as SQL-87) was published as the second version of the SQL standard, incorporating enhancements and clarifications.
   • Subsequent versions of the SQL standard were released in 1989 (SQL-89) and 1992 (SQL-92), with each version introducing new features and improvements.
   • The SQL-92 standard, in particular, established SQL as the de facto language for relational databases and laid the groundwork for modern SQL implementations.
5. 2000s-Present: Evolution and Adoption:
   • Since the 1990s, SQL has continued to evolve with new versions of the SQL standard being released periodically, including SQL:1999, SQL:2003, SQL:2008, SQL:2011, and SQL:2016.
   • These standards have introduced features such as recursive queries, window functions, common table expressions, and XML support, among others.
   • SQL has become the standard language for interacting with relational databases and is supported by a wide range of database management systems, including open-source databases like MySQL, PostgreSQL, and SQLite, as well as commercial offerings like Microsoft SQL Server and Oracle Database.

Overall, SQL has played a crucial role in the development and adoption of relational database technology, providing a powerful and standardized way to query and manipulate data. Its continued evolution reflects the ongoing demand for efficient and reliable data management solutions in various industries.